The present invention relates to a method for operating a radio communication system, wherein a radio station decides about the assignment of radio resources to a user terminal.
In radio communication systems, messages containing information such as speech, video data, SMS (Short Message Service), MMS (Multimedia Messaging Service), remote control, etc. are transmitted over an air interface between radio stations. The transmission can be both bidirectional and unidirectional. Radio stations receiving and/or transmitting messages can be part of the network infrastructure, being e.g. base stations, repeaters, access points; on the other hand, radio stations being user terminals exist. In a mobile radio communication system, at least some user terminals are mobile radio stations. For transmitting messages, carrier frequencies available to the respective radio communication system are used.
Current mobile radio communication systems are oftentimes cellular systems designed e.g. according to the standard GSM (Global System for Mobile Communication) or UMTS (Universal Mobile Telecommunications System), having network infrastructure components comprising amongst others base stations and devices for controlling the base stations. A further example of a radio communication system is a broadband system with wireless access, e.g. according to IEEE 802.16. Future systems may be evolutions of UMTS, referred to as LTE (Long Term Evolution), fourth generation systems, or ad-hoc networks. Besides the wide-ranging cellular systems, wireless local networks like WLANs, HiperLAN systems, DECT systems, IEEE 802.11 systems, Bluetooth systems, and WATM systems can be deployed.
Different multiple access techniques exist in order to allow user terminals to access the radio resources. Multiple access techniques allow for a partitioning of radio resources in the time domain (Time Division Multiple Access, TDMA), in the frequency domain (Frequency Division Multiple Access, FDMA), in the code domain (Code Division Multiple Access, CDMA), and in the space domain (Space Division Multiple Access, SDMA). Preferably combinations of different multiple access techniques are applied, such as the combination of a FDMA and a CDMA technique.
In order to make an especially efficient transmission of information possible, a frequency band can be subdivided into a multiplicity of subbands. This method permits to transmit several narrowband signals instead of one broadband signal, having the advantage of reducing the complexity on the receiver end. Furthermore, by using subbands radio resources can be assigned to user terminals with high granularity. The latter is especially beneficial for transmissions with varying data rates. OFDM (Orthogonal Frequency Division Multiplexing), an example of a multicarrier transmission method, uses approximately rectangular pulse shapes in the time domain. Looking at a certain subband, as a result of the choice of the width of OFDM-subbands, the signals of the other subbands have a zero crossing in the middle of the certain subband, so that the OFDM-subbands are orthogonal to each other. In case narrow subbands are used, the signal transmission of the single subbands is normally not frequency selective.
In case a first radio station communicates using first radio resources, and a second radio station communicates using the same or similar radio resources, interference between the two communications is generated. In order to avoid this interference, radio resource management can be applied.